The present disclosure relates to a control system, a control apparatus and a control method. More particularly, the present disclosure relates to a control system, a control apparatus and a control method for efficiently extracting electric power from an electric generator whose terminal voltage exhibits a fluctuation such as a solar cell.
In recent years attention is paid to natural energy also called clean energy, which emits no air pollution offender upon electric power generation.
The natural energy is electric power obtained, for example, by photovoltaic power generation, solar thermal power generation, wind power generation or the like. Also it is attempted actively to extract electric energy from kinetic energy generated by human activities although the generated power is low in comparison with that by photovoltaic power generation and so forth.
Incidentally, a solar cell has a characteristic that the voltage and the current to be extracted therefrom depend upon the power consumption required by a load connected thereto. For example, if a solar cell is used to charge a battery, then the current to be extracted from the solar cell depends upon the voltage required by the battery.
Therefore, if the electric power accepted by the load connected to the solar cell is inappropriate, then the generated power obtained from the solar cell suffers from some loss. The characteristic that, since the voltage and the current to be extracted depend upon the power consumption required by the load connected to the solar cell, the electric power obtained by the electric power generation is not fixed commonly applies also to an electric generator which uses wind power.
Further, for example, in the case of photovoltaic power generation, the electric power obtained by the electric power generation sometimes fluctuates suddenly by a variation in illumination intensity upon or a variation in temperature of the solar cell.
Therefore, in order to extract power efficiently and stably from a solar cell, generally a power conditioner having a maximum power point tracking (MPPT) controlling function is interposed between the solar cell and the load. According to the MPPT control, a voltage value with which the product of the current and the voltage extracted from the solar cell is maximized is determined successively by calculation. Then, the terminal voltage of the solar cell is changed so that the generated electric power obtained by the electric power generation from the solar cell may be maximized.
Although the MPPT control is superior in that electric power is extracted efficiently from the solar cell, since the calculation includes multiplication, also the load of the calculation is high. Further, since time is required for the calculation, the MPPT control is not easy to deal with a sudden variation of the illumination intensity upon the solar cell or the like.
Therefore, control by a voltage tracking method which can be implemented by a circuit which is simple in comparison with that by the MPPT control is sometimes applied. It is to be noted that Japanese Patent Laid-open No. 2009-017686 discloses that output current of a charge controlling IC (Integrated Circuit) for a lithium battery is fed back to a controlling program terminal to control the maximum voltage of the solar cell to a fixed voltage.